package com.hugegis.SmarHMETER;

import java.io.IOException;
import java.util.ArrayList;

/*************************************************************************
 * Compilation: javac CRC16.java <br>
 * Execution: java CRC16 s
 * 
 * <br>
 * Reads in a string s as a command-line argument, and prints out its 16-bit
 * Cyclic Redundancy Check (CRC16). Uses a lookup table.
 * 
 * <p>
 * Reference: http://www.gelato.unsw.edu.au/lxr/source/lib/crc16.c
 * 
 * 
 * <p>
 * Uses irreducible polynomial: 1 + x^2 + x^15 + x^16
 * 
 * 
 *************************************************************************/

public class CRC16 {
	private final static int crc16Tab[] = { /* CRC polynomial 0xA001 */
	0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6,
			0x74C7, 0x44A4, 0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823, 0xC9CC,
			0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B, 0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A,
			0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83B9,
			0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F,
			0xF77E, 0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634, 0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A, 0x4A75,
			0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8, 0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93,
			0x3EB2, 0x0ED1, 0x1EF0};

	/**
	 * make CRC code
	 * 
	 * @param bufIn
	 *            source byte stream
	 * @return crc16 (unsingned short)
	 * @throws IOException
	 */
	public static int makeCRC16(byte[] bufIn) {
		return makeCRC16(bufIn, 0, bufIn.length);
	}

	/**
	 * make CRC code
	 * 
	 * @param bufIn
	 *            source byte stream
	 * @param length
	 *            length of handling stream
	 * @return crc16 (unsingned short)
	 * @throws IOException
	 */
	public static int makeCRC16(byte[] bufIn, int length) {
		return makeCRC16(bufIn, 0, length);
	}

	/**
	 * make CRC code
	 * 
	 * @param bufIn
	 *            source byte stream
	 * @param start
	 *            starting point of handling
	 * @param length
	 *            length of handling stream
	 * @return crc16 (unsingned short)
	 * @throws IOException
	 */
	public static int makeCRC16(byte[] bufIn, int start, int length) {
		int com_val, accum, i;
		accum = 0x00;

		for (i = 0; i < length; i++) {
			com_val = (accum >> 8) ^ (bufIn[i + start] & 0x00FF);
			com_val = com_val & 0xFFFF;
			accum = (accum << 8) ^ (crc16Tab[com_val] & 0xFFFF);
			accum = accum & 0xFFFF;
		}
		return accum;
	}

	public static int makeCRC16(ArrayList<Byte> arraylist, int start, int length) {
		int com_val, accum, i;
		accum = 0x00;

		for (i = 0; i < length; i++) {
			com_val = (accum >> 8) ^ (arraylist.get(i + start) & 0x00FF);
			com_val = com_val & 0xFFFF;
			accum = (accum << 8) ^ (crc16Tab[com_val] & 0xFFFF);
			accum = accum & 0xFFFF;
		}
		return accum;
	}

	/**
	 * Check stream by crc16 code Comparing target is
	 * bufIn[bufIn.length-2]*0x0100+buf[bufIn.length-1]
	 * 
	 * @param bufIn
	 *            source byte stream
	 * @return true if bufIn is valid
	 * @throws IOException
	 */
	public static boolean checkCRC16(ArrayList<Byte> arraylist) {
		return checkCRC16(arraylist, 0, arraylist.size() - 2);
	}

	/**
	 * Check stream by crc16 code Comparing target is
	 * bufIn[length]*0x0100+buf[length+1]
	 * 
	 * @param bufIn
	 *            source byte stream
	 * @param length
	 *            length of handling stream
	 * @return true if bufIn is valid
	 * @throws IOException
	 */
	public static boolean checkCRC16(ArrayList<Byte> arraylist, int length) {
		return checkCRC16(arraylist, 0, length);
	}

	/**
	 * Check stream by crc16 code Comparing target is
	 * bufIn[length]*0x0100+buf[length+1]
	 * 
	 * @param bufIn
	 *            source byte stream
	 * @param start
	 *            starting point of handling
	 * @param length
	 *            length of handling stream
	 * @return true if bufIn is valid
	 * @throws IOException
	 */

	public static boolean checkCRC16(ArrayList<Byte> arraylist, int start, int length) {
		int com_val, accum, i;
		accum = 0x00;

		for (i = 0; i < length; i++) {
			com_val = (accum >> 8) ^ (arraylist.get(i + start) & 0x00FF);
			com_val = com_val & 0xFFFF;
			accum = (accum << 8) ^ (crc16Tab[com_val] & 0xFFFF);
			accum = accum & 0xFFFF;
		}
		if ((byte) ((accum & 0xff00) >> 8) == arraylist.get(length + 2)) {
			if (((byte) (accum & 0x00ff) == arraylist.get(length + 3))) {
				return true;
			} else {
				return false;
			}
		} else {
			return false;
		}
	}
}
